(1) Field of the Invention
The present invention relates to a solid-state image sensing apparatus composed of a solid-state image sensing device, which converts received light into electric signals, and a signal processing circuit.
(2) Description of the Related Art
One of most eagerly developed apparatuses in recent years might be solid-state image sensing apparatuses, which include a solid-state image sensing device for converting received light into electric signals, and a signal processing circuit for converting the electric signals into image signals.
The solid-state image sensing apparatuses are largely used in digital cameras, such as digital still cameras and digital video cameras. There has always been a strong demand for improving image quality of digital cameras, and the pixel resolution for the solid-state image sensing devices has been improved at a rapid pace.
Digital cameras use less pixels for shooting moving images than for taking still pictures, due to limited speeds at which image signals are output. In some methods proposed to achieve this, the solid-state image sensing devices output data of a reduced number of pixels, compared with the number of pixels for which it read signal charges initially.
Patent Document 1 (Japanese Laid-Open Patent Application No. H11-234688), for example, discloses a method for driving a solid-state image sensing device in which every three pixels aligned sequentially in the horizontal direction are regarded as one block, signal charges of two pixels except for the middle one (i.e. two at both ends of the block) are mixed together, and the signal charge of the middle pixel of a block is mixed with that of the middle pixel of an adjacent block. In this way, this driving method allows the solid-state image sensing device to output image signals of a predetermined number of pixels that have been reduced in the horizontal direction.
However, if one third of the components of the image signals is reduced as described above, one third of the sampling frequency, which is not 0 in the conventional driving methods, is added to the DC (Direct Current) component of the signals. This generates moire or false signals, degrading the image quality represented by the output image signals.
[PATENT DOCUMENT 1]: Japanese Laid-Open Patent Application No. H11-234688